Here is the full list of all 66 Alien Swarm achievements.
Complete the Jacob's Rest campaign on Easy difficulty or harder.
Deploy 10 ammo stashes that are used by other marines.
Kill 6 Swarm with a single Grenade.
Deliver the finishing blow to a Swarm Shieldbug.
Complete a mission with better than 90% accuracy.
Kill 250 Swarm with the Assault Rifle.
Kill 5 Swarm with explosive barrels in a single mission.
Roll under a Swarm Ranger projectile.
Kill a Swarm Boomer before it inflates.
Successfully perform 5 fast reloads in a row.
Complete 2 co-op missions online. Earns a Team Fortress 2 parasite hat.
Finish a mission without the tech getting killed.
Guard the squad's tech so that he takes no damage during the hack.
Successfully perform a fast reload.
Kill 25 drones without friendly fire. Four marines must be present in the mission.
Complete a mission with no friendly fire incidents. Four marines must be present in the mission.
Complete a mission on Normal difficulty or harder without receiving any damage.
Destroy all Swarm Eggs in a mission without allowing any to hatch.
Kill 100 Swarm Grubs.
Kill a Swarm Parasite with a melee attack.
Kill 20 Swarm with melee attacks in a single mission.
Cure an Infested marine.
Complete 10 wire hacks without access being logged.
Complete 10 computer hacks without access being logged.
Heal all 4 marines with a single Heal Beacon.
Kill 15 Swarm with all four marines under the effects of a Damage Amp in a single mission.
Heal 300 points of damage in a single mission without dealing any non-melee damage to the Swarm.
Stun 6 Swarm with a single Stun Grenade.
Seal a door with the welder.
Freeze 6 Swarm with a single Freeze Grenade.
Kill 500 Swarm with deployable Sentry Guns.
Kill 250 Swarm with a Prototype Rifle.
Kill 250 Swarm with an Autogun.
Kill 250 Swarm with a Shotgun.
Kill 250 Swarm with a Vindicator.
Kill 250 Swarm with Twin Pistols.
Kill 250 Swarm with PDWs.
Kill 250 Swarm with a Tesla Cannon.
Kill 250 Swarm with a Rail Rifle.
Kill 250 Swarm with a Flamethrower.
Kill 250 Swarm with a Chainsaw.
Kill 250 Swarm with a Minigun.
Kill 250 Swarm with a Marksman Rifle.
Kill 250 Swarm with a Grenade Launcher.
Kill 100 Swarm with Hornet Barrages.
Kill 100 Swarm with Laser Tripmines.
Kill 100 Swarm with Incendiary Mines.
Unlock all the available weapons.
Complete the Jacob's Rest campaign on Normal difficulty or harder.
Complete the Jacob's Rest campaign on Hard difficulty or harder.
Awarded for finishing the Jacob campaign on Insane difficulty.
Kill 1,000 Swarm.
Kill 5,000 Swarm.
Kill 25,000 Swarm.
Kill 100,000 Swarm.
Complete Landing Bay within 1:25 on Normal difficulty or harder without any marines dying.
Complete Cargo Elevator within 2:50 on Normal difficulty or harder without any marines dying.
Complete Deima Surface Bridge within 2:30 on Normal difficulty or harder without any marines dying.
Complete Rydberg Reactor within 3:10 on Normal difficulty or harder without any marines dying.
Complete SynTek Residential within 2:30 on Normal difficulty or harder without any marines dying.
Complete Sewer Junction within 1:30 on Normal difficulty or harder without any marines dying.
Complete Timor Station within 4:25 on Normal difficulty or harder without any marines dying.
Complete a campaign on Normal difficulty or harder without any marines dying.
Complete a mission on Normal difficulty or harder without any marines dying.
Awarded for finishing the Jacob campaign on Brutal difficulty.
Complete any mission on Brutal difficulty with Onslaught and Hardcore Friendly Fire enabled.